Dump truck

ABSTRACT

A dump truck includes a suspension and a steering mechanism. The suspension includes: a suspension arm in a form of an upper arm having an up-and-down movable proximal end supported on a vehicle body frame; and a tire support in a form of a casing rotatably attached to a distal end of the upper arm. The steering mechanism includes a steering cylinder having a proximal end attached to the upper arm and a distal end attached to a knuckle arm provided to the tire support.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No.PCT/JP2014/054978 filed on Feb. 27, 2014, the contents of which areincorporated herein in their entirety.

TECHNICAL FIELD

The present invention relates to a dump truck, for instance, alarge-sized driverless off-road dump truck.

BACKGROUND ART

A large-sized dump truck working in mines and the like has beentypically known. As a steering mechanism of front wheels (steeringwheels) of such a dump truck, there has been typically known a steeringmechanism including a yoke that is a part of a suspension and has aup-and-down movable proximal end supported on a vehicle body frame, areceiving seat rotatably attached to a distal end of the yoke, a knucklearm attached to the receiving seat, and a steering cylinder extendingbetween the knuckle arm and the vehicle body frame to connect theknuckle arm and the vehicle body frame (for instance, Patent Literature1).

Moreover, an off-road dump truck has also been known for having steeringwheels as all the tires in order to improve delivery performance (forinstance, Patent Literatures 2 and 3).

CITATION LIST Patent Literatures

Patent Literature 1: JP-A-5-193373

Patent Literature 2: U.S. Pat. No. 6,578,925

Patent Literature 3: U.S. Pat. No. 6,783,187

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In Patent Literature 1, since a proximal end of the steering cylinder isconnected to the vehicle body and a distal end of the steering cylinderis connected to the knuckle arm, when the receiving seat moves up anddown in conjunction with the yoke in an operation of the suspension, theknuckle arm attached to the receiving seat also moves up and down toslightly change a distance between the vehicle body and the knuckle arm.Accordingly, this change affects an advance and retraction amount of thesteering cylinder to cause an unstable steering amount of the tireduring the up-and-down motion of the receiving seat.

Patent Literatures 2 and 3 in which a four-wheel steering is employedfail to specifically disclose the steering mechanism.

An object of the invention is to provide a dump truck having a steeringmechanism capable of obtaining a desired steering amount withoutreceiving an influence from an up-and-down motion of a suspension.

Means for Solving the Problems

According to an aspect of the invention, a dump truck includes a vehiclebody frame; a suspension; a steering mechanism; tires suspended from thevehicle body frame via the suspension and configured to be steered bythe steering mechanism and travel the dump truck; and a body supportedby the vehicle body frame and configured to be raised and lowered, thesuspension including: a suspension arm having a up-and-down movableproximal end supported on the vehicle body frame; and a tire supportrotatably attached to a distal end of the suspension arm, the steeringmechanism including: a steering cylinder having a proximal end attachedto the suspension arm and a distal end attached to a knuckle armprovided to the tire support.

According to the above aspect of the invention, since the steeringcylinder is attached to connect the knuckle arm and the suspension arm,a positional relationship between which is hardly changed in anup-and-down motion direction during the up-and-down motion of thesuspension, even when the suspension moves up and down during itsoperation, such a change does not affect an advance and retractionamount of the steering cylinder, so that a steering amount of the tirescan be stabilized to provide a desired steering amount.

In the above aspect, it is preferable that the suspension arm includesan upper arm and a lower arm that are attached to the vehicle body framesuch that the upper arm is arranged above the lower arm, and theproximal end of the steering cylinder is attached to the upper arm.

With this arrangement, since the steering cylinder is disposed at a highposition in the same manner as the upper arm, the steering cylinder canbe kept from being hit by gravel and the like on a road to preventdamage of the steering cylinder.

In the above aspect, it is preferable that the vehicle body frameincludes a support that supports the suspension arm such that thesuspension arm is movable up and down, the suspension arm includes asteering cylinder attachment arm extending over the support and furtherextending inward in a vehicle width direction, and the proximal end ofthe steering cylinder is attached to the steering cylinder attachmentarm.

With this arrangement, since the proximal end of the steering cylinderis attached to the steering cylinder attachment arm extending inward inthe vehicle body frame among the suspension arm, a sufficient distancefrom this attachment position to an attachment position of the steeringcylinder to the knuckle arm can be ensured. Accordingly, since thesteering cylinder to be used is sufficiently long in an axial direction,the maximum steering amount (maximum steering angle) can be increased toimprove a rotation performance.

In the above aspect, it is preferable that, viewed in a traveldirection, the steering cylinder has an axial line overlapping a linepassing through a rotation center of the suspension arm and the tiresupport and traversing a motion center of the suspension arm on thevehicle body frame.

With this arrangement, respective up-and-down motion regions to berequired for respective up-and-down motions of the suspension arm andthe steering cylinder can be the same when viewed in the traveldirection, so that suspension arm and the steering cylinder can beeasily prevented from interfering with other members.

In the above arrangement, it is preferable that the vehicle body frameincludes a cross member provided in the vehicle width direction, thecross member supports a lower end of a hoist cylinder configured toraise and lower the body, and the steering cylinder is disposed oppositethe hoist cylinder across the cross member in the travel direction.

With this arrangement, the hoist cylinder body that is requisite forraising and lowering the body can be reliably avoided from interferingwith the steering cylinder.

According to another aspect of the invention, a dump truck includes avehicle body frame; a suspension; a steering mechanism; tires suspendedfrom the vehicle body frame via the suspension and configured to besteered by the steering mechanism and travel the dump truck; and a bodysupported by the vehicle body frame and configured to be raised andlowered, the suspension including: an upper arm having an up-and-downmovable proximal end supported on an upper support provided to thevehicle body frame; a lower arm having an up-and-down movable proximalend supported on a lower support provided to the vehicle body frame; anda tire support rotatably attached between respective distal ends of theupper and lower arms, in which the upper arm includes a steeringcylinder attachment arm extending over the support and further extendinginward in a vehicle width direction, the steering mechanism includes asteering cylinder having a proximal end attached to the steeringcylinder attachment arm and a distal end attached to a knuckle armprovided to the tire support, and viewed in the travel direction, thesteering cylinder has an axial line overlapping a line passing through arotation center of the upper arm and the tire support and traversing amotion center of the upper arm on the vehicle body frame.

According to the above aspect of the invention, the same advantages asthose of the above-described invention having the same arrangement canbe obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partially-exploded perspective view of a dump truckaccording to an exemplary embodiment of the invention.

FIG. 2 is a side view of the dump truck.

FIG. 3 is an illustration of the dump truck in a travel direction, whichis viewed in a direction indicated by an arrow III in FIG. 2.

FIG. 4 is a plan view of the dump truck.

FIG. 5 is a cross-sectional view showing a suspension, which is viewedin a direction indicated by an arrow V-V in FIG. 4.

FIG. 6 is a schematic illustration for explaining an intersection angle.

FIG. 7 is a cross-sectional view showing a steering mechanism, which isviewed in a direction indicated by an arrow VII-VII in FIG. 4.

FIG. 8 is a cross-sectional view showing a support structure and acooling structure of an electric motor.

FIG. 9 is a plan view showing a layout of devices.

FIG. 10 is a perspective view showing an overall support frame.

FIG. 11 is an illustration of an attachment position of a hoist cylinderin the travel direction, which is viewed in a direction indicated by anarrow XI-XI in FIG. 4.

FIG. 12 is a side view showing the attachment position of the hoistcylinder.

DESCRIPTION OF EMBODIMENT(S)

Exemplary embodiment(s) of the invention will be described below withreference to the attached drawings.

FIGS. 1 to 4 are respectively a partially-exploded perspective view, aside view, an illustration of the dump truck in a travel direction,which is viewed in a direction indicated by an arrow III in FIG. 2, anda plan view of a dump truck according to an exemplary embodiment of theinvention.

X, Y and Z axes in the drawings are orthogonal to each other in theexemplary embodiment. For convenience of the explanation, in theexemplary embodiment, with reference to FIG. 1, a first travel directionof the dump truck 1 is defined as an arrow direction of the X axis whilea second travel direction thereof is defined as an opposite direction ofthe arrow direction of the X axis, a first vehicle width direction ofthe dump truck 1 is defined as an arrow direction of the Y axis while asecond vehicle width direction thereof is defined as an oppositedirection of the arrow direction of the Y axis, and a first verticaldirection of the dump truck 1 is defined as an arrow direction of the Zaxis while a second vertical direction thereof is defined as an oppositedirection of the arrow direction of the Z axis. Moreover, in thefollowing exemplary embodiment, the first travel direction, the secondtravel direction, the first vehicle width direction and the secondvehicle width direction are sometimes respectively referred to as“front,” “rear (back),” “right” and “left”.

Overall Description of Dump Truck

As shown in FIG. 1, a dump truck 1 is a driverless off-road dump truckconfigured to travel by remote control. For instance, the dump truck 1is a vehicle working at a mining site for developing mines. The remotecontrol is performed fully using information communication technologysuch as a communication means set at a control center and the dump truck1 and GPS (Global Positioning System).

The dump truck 1 includes a vehicle body 10 configured to travel withuse of a pair of left and right tires 11, 11 and a pair of left andright tires 12, 12, the tires 11, 11 being set on bothvehicle-width-directional sides of the vehicle body 10 in the firsttravel direction, the tires 12, 12 being set on bothvehicle-width-directional sides of the vehicle body 10 in the secondtravel direction. The vehicle body 10 includes: a vehicle body frame 20extending along the travel direction and to which the tires 11, 12 areprovided; a load-carrying body 30 that is supported by the vehicle bodyframe 20 and configured to be raised and lowered (see a two-dot chainline in FIG. 2; devices 41 to 49 mounted on the vehicle body frame 20; asuspension 50 by which the tires 11, 12 are suspended from the vehiclebody frame 20; and a steering mechanism. The dump truck 1, which is avehicle dedicated for remote control, does not include a cab for adriver to operate, which is provided in a typical dump truck.

Explanation of Vehicle Body Frame

The vehicle body frame 20 will be described in details below.

As shown in FIGS. 2 to 4, the vehicle body frame 20 includes: a lowercross member 201 (i.e., a lower one of cross members) provided atpositions of the right and left tires 11 in the first travel direction(i.e., the right and left tires 11 provided to a first side of thevehicle body frame 20 in the travel direction) and extending in thevehicle width direction; a pair of right and left vertical members 202,202 standing upward on both ends of the lower cross member 201; and anupper cross member 203 (i.e., an upper one of the cross members)extending in the vehicle width direction in a manner to connect upperends of the respective vertical members 202. Among the above members,the pair of vertical members 202 and the upper cross member 203 define afirst vertical frame 21 that vertically stands at the positions of theright and left tires 11 and has a portal shape viewed in the traveldirection of the vehicle body 10 (see FIG. 3).

In other words, the vehicle body frame 20 in a side view includes thefirst vertical frame 21 that vertically stands at the positions of thetires 11 provided to the first side of the vehicle body frame 20.

The vehicle body frame 20 also includes: the lower cross member 201provided at positions of the right and left tires 12 in the secondtravel direction (i.e., the right and left tires 12 provided to a secondside of the vehicle body frame 20 in the travel direction) and extendingin the vehicle width direction; a pair of right and left verticalmembers 202, 202 standing upward on both ends of the lower cross member201; and an upper cross member 203 extending in the vehicle widthdirection in a manner to connect upper ends of the respective verticalmembers 202. Among the above members, the pair of vertical members 202and the upper cross member 203 define a second vertical frame 22 thatvertically stands at the positions of the right and left tires 12 andhas a portal shape viewed in the travel direction of the vehicle body10.

In other words, the vehicle body frame 20 in a side view includes thesecond vertical frame 22 that vertically stands at the positions of thetires 12 provided to the second side of the vehicle body frame 20.

The first vertical frame 21 and the second vertical frame 22 havesubstantially the same shape.

Ends of the front lower cross member 201 are connected to ends of theback lower cross member 201 by a pair of right and left lower sidemembers 23, 23 disposed in parallel to each other in the traveldirection and spaced from each other in the vehicle width direction. Avertical middle of the first vertical frame 21 is connected to avertical middle of the second vertical frame 22 by a pair of right andleft upper side members 24, 24 positioned above the lower side members23, 23 (see FIG. 2).

Side members 25, 25 of a short length, which are respectively positionedon extension lines of the lower side members 23, 23, extend in the firsttravel direction from a lower portion of the first vertical frame 21.Ends of the respective side members 25, 25 are connected by a crossmember 26. Side members 27, 27 of a short length, which are respectivelypositioned on extension lines of the lower side members 23, 23, extendin the second travel direction from a lower portion of the secondvertical frame 22. Ends of the respective side members 27, 27 areconnected by a cross member 28 along the vehicle width direction (seeFIG. 4).

As shown in FIGS. 3 and 5, the lower cross member 201 on which the firstvertical frame 21 stands is shaped in a hollow cylinder. Electric motors43, 43 configured to independently respectively drive the tires 11, 11via a drive shaft 18 are housed at both sides of an inside of the lowercross member 201. In the exemplary embodiment in which all the tires 11,12 are to be driven, a pair of electric motors 43, 43 are also housed inthe same manner as the above within the lower cross member 201 on whichthe second vertical frame 22 stands and are configured to independentlyrespectively drive the tires 12. A final reduction gear 14 (a planetgear mechanism) is disposed between an end of the drive shaft 18 and atire wheel.

An upper surface of the upper cross member 203 defining an upper portionof the first vertical frame 21 and an upper portion of the secondvertical frame 22 is defined as a mount portion 204 that is a concavecurve with a predetermined curvature. The body 30 is mounted only on themount portion 204. A suspension support 205 supporting an upper end of asuspension cylinder 53 (a part of the suspension 50) is provided at eachend of the upper cross member 203. A lower end of the suspensioncylinder 53 is connected to an upper arm 51 (a part of the suspension50). With this arrangement, the mount portion 204 is positioned on anaxial line 53A of the suspension cylinder 53 configured to transmit aload downward (see FIG. 3).

The suspension 50 will be described later.

Herein, the load to be transmitted to a road surface through the tires11, 12 includes a carrying load and a vehicle body load. The carryingload means a load defined by a weight of the body 30 loaded with goods.The vehicle body load means a load defined by a weight of the vehiclebody 10 excluding weights of the tires 11, 12 and the body 30. In theexemplary embodiment, the vehicle body load and the carrying load aresometimes collectively referred to as an entire load.

Accordingly, the carrying load is transmitted from the mount portion 204to the road surface through the suspension 50 (including the suspensioncylinder 53) beneath the mount portion 204 and the tires 11, 12. Thus,the carrying load is transmitted through a short and simple transmissionpath (see dotted lines in FIGS. 2 and 3). In other words, the carryingload is transmitted without acting on the upper side member 24, thelower side member 23 and the like.

A shape of the entire vehicle body frame 20 is substantiallyplane-symmetrical to a vertical plane including a first center line 10Apassing through the middle between the front tires 11 and the rear tires12 and extending in the vehicle width direction, while beingsubstantially plane-symmetrical to a vertical plane including a secondcenter line 10B being orthogonal to the first center line 10A andextending in the travel direction through the middle between the tiresin the vehicle width direction (see FIGS. 1 and 4).

Moreover, a support frame 81 is provided on the first center line 10A inthe vehicle body frame 20 in a manner to bridge over the vehicle bodyframe 20 in the vehicle width direction. The support frame 81 isprovided for supporting the devices 44 to 48 on the vehicle body frame20. As shown in FIGS. 1, 9 and 10, the support frame 81 includes a pairof front and back sub frames 82 spaced from each other in the traveldirection. The entire support frame 81 is shaped in a form of a saddle.Both sides of the support frame 81 project between the pair of front andback tires 11 and 12 on both the right and left sides of the vehiclebody frame 20. Accordingly, the devices 44 to 48 supported by thesupport frame 81 are also disposed between the pair of front and backtires 11 and 12.

Specific disposition of the devices 44 to 48 will be described later.

Each of the sub frames 82 includes: a pair of right and left L-shapedframes 85 each including vertical portions 83 that are each fixed to thelower side member 23 and the upper side member 24 at both sides of thevehicle width direction and extensions 84 respectively horizontallyextending toward the outside of the vehicle body frame 20 from lowerends of both the vertical portions 83 in the vehicle width direction; anupper connecting portion 86 connecting upper ends of the verticalportions 83 of the pair of right and left L-shaped frames 85 above theupper side member 24; and a lower connecting portion 87 connecting therespective lower ends of the vertical portions 83 of the pair of rightand left L-shaped frames 85 under the lower side member 23.

The L-shaped frames 85 are detachably fixed to the lower side members 23and the upper side member 24 s with an unillustrated fastening unit(e.g., a bolt). The upper ends of the vertical portions 83 in each ofthe L-shaped frames 85 are detachably connected to the upper connectingportion 86 with a pin. The lower ends of the vertical portions 83 ineach of the L-shaped frames 85 are detachably connected to the lowerconnecting portion 87 with a pin. Accordingly, the connection of each ofthe L-shaped frames 85 to the connecting portions 86 and 87 is providedby a flexible connection with a pin while each of the L-shaped frames 85to the vehicle body frame 20 is kept firmly fixed, so that the L-shapedframes 85 can favorably tolerate torsion or the like of the vehicle bodyframe 20.

Explanation of Body

As shown in FIGS. 1 to 3, a depth of the body 30 is the maximum at amiddle portion thereof in the travel direction and is decreased towardboth the sides thereof in the travel direction and both the sidesthereof in the vehicle width direction. Specifically, the body 30include: a slant bottom 31 that defines the depth deeper toward themiddle of the body 30; and side faces 32, 32 that guard respective edgesof longer sides of the bottom 31 in the travel direction. On slantparts, which are slant in different directions, of a lower surface ofthe bottom 31, horizontal ribs 33, 33 are provided in a manner totraverse the slant parts in the vehicle width direction and so that endsof each of the horizontal ribs 33, 33 extend to outer faces of the sidefaces 32, 32.

The horizontal ribs 33 are mounted on the respective mount portions 204of the first vertical frame 21 and the second vertical frame 22. Each ofthe horizontal ribs 33 is curved at the same curvature as that of themount portion 204 so that the horizontal ribs 33 are respectively inclose contact with the mount portions 204. Moreover, a pair of verticalribs 34, 34 are provided in parallel in the travel direction on thelower surface of the bottom 31. The body 30 is mounted on the mountportion 204 at positions where the vertical ribs 34 intersect with thehorizontal ribs 33 (see FIGS. 2 and 3).

Respective attachment portions 36, 36 to which upper ends of a pair ofhoist cylinders 35, 35 are attached are provided on one of the slantparts of the lower surface of the bottom 31 (see FIGS. 1, 11 and 12).The hoist cylinders 35 are hydraulic actuators for raising and loweringthe body 30. Lower ends of the hoist cylinders 35 are attached to thelower cross member 201 on which the second vertical frame 22 stands. Inthe middle of the one of the slant parts, a pair of pivot shafts 37, 37connecting the body 30 to the vehicle body frame 20 so that the body 30is pivotable are provided (only one of the pivot shafts 37, 37 is shownin FIGS. 2 and 12). The pivot shafts 37 are respectively supported onbody supports 206, 206 extending from upper portions of the verticalmembers 202 to the upper cross member 203. Since the second verticalframe 22 stands at the position of the right and left tires 12 in a sideview, in terms of the support position of the body 30 in the traveldirection, the body 30 is supported on the vehicle body frame 20 at theposition of the right and left tires 12 through the body support 206.

A shape of the entire body 30 is also substantially plane-symmetrical tothe above-described vertical plane including the first center line 10Aand substantially plane-symmetrical to the above-described verticalplane including the second center line 10B (see FIG. 1). The body 30 ismounted in the middle of the vehicle body frame 20 that isplane-symmetrical to the vertical plane including the first center line10A and the second center line 10B. Consequently, a load distribution ofthe carrying load to be transmitted from the mount portion 204 of thevehicle body frame 20 to the tires 11 and 12 becomes equal. In otherwords, an entire load obtained by combining the vehicle load and thecarrying load is transmitted to the tires 11, 12 at an even loaddistribution.

Explanation of Devices

Main devices shown in FIG. 1 are an engine 41, a generator motor 42 anda hydraulic pump (not shown) configured to be driven by an output of theengine 41, an electric motor 43 configured to be driven by electricenergy generated by the generator motor 42 (see FIGS. 2 and 3), a firstradiator 44 configured to radiate heat of a cooling water of the engine41, a first cooling fan 45 configured to supply a cooling air to thefirst radiator 44, a second radiator 46 for a water-cooling typeaftercooler 41A (see FIG. 9) configured to cool charge air deliveredfrom an air cleaner through a supercharger to the engine 41, a secondcooling fan 47 configured to supply a cooling air to the second radiator46, a pair of brake resistors 48, 48 configured to convert kineticenergy of the tires 11, 12 to electric energy to generate Joule heat, ahydraulic fluid tank (not shown) configured to store a hydraulic fluidpumped from the hydraulic pump, and a pair of front and rear controllers49, 49 configured to totally control travel of the dump truck 1.

Specific disposition of the devices 41 to 49 will be described later.

Explanation of Suspension

FIG. 5 is a cross-sectional view showing the suspension 50, which isviewed in a direction indicated by an arrow V-V in FIG. 4

As shown in FIGS. 3 to 5, an independent double-wishbone-type suspensionis employed as the suspension 50. The suspension 50 includes:substantially horizontal upper arm 51 and lower arm 52 each havingup-and-down movable proximal ends supported by the vehicle body frame20; a tire support in a form of a cylindrical casing 56 having an upperportion rotatably connected to a distal end of the upper arm 51 and alower portion rotatably connected to a distal end of the lower arm 52;and a suspension cylinder 53 having an upper end rotatably connected tothe vehicle body frame 20 and a lower end rotatably connected to theupper arm 51. The suspension cylinder 53 absorbs and attenuates impactsto the tires 11, 12 while transmitting the vehicle body load and thecarrying load to the tires 11, 12. The casing 56 rotates and supportsthe tires 11, 12 through a final reduction gear 14. In the exemplaryembodiment, the upper arm 51 and the lower arm 52 define a suspensionarm according to the invention.

Specifically, a pair of proximal ends of the upper arms 51 having abifurcated shape in a plan view are rotatably supported by the supportin a form of an upper support 207 provided on a lower portion of thevertical member 202 of each of the first vertical frame 21 and thesecond vertical frame 22. A pair of proximal ends of the lower arm 52having a bifurcated shape in a plan view are rotatably supported by alower support 208 provided on a lower end of the lower cross member 201on which each of the first vertical frame 21 and the second verticalframe 22 stands.

A distal end of the upper arm 51 is connected to an upper ball joint 57provided to the upper portion of the casing 56. A distal end of thelower arm 52 is connected to a lower ball joint 58 provided to the lowerportion of the casing 56. A top of the upper ball joint 57 is coveredwith a connecting bracket 54 fixed to an upper surface of the upper arm51. The connecting bracket 54 is connected by the suspension cylinder 53to the suspension support 205 of each of the first vertical frame 21 andthe second vertical frame 22. At this time, the lower end of thesuspension cylinder 53 is connected to the connecting bracket 54 at aposition very close to the upper ball joint 57.

A king pin shaft 56A connecting a rotation center 57A of the upper balljoint 57 to a rotation center 58A of the lower ball joint 58 intersectswith an axial line 53A of the suspension cylinder 53 at a connectingportion of the upper ball joint 57 of the casing 56 and the upper arm51, specifically, within a range of a ball diameter of the upper balljoint 57, more specifically at a rotation center 57A of the upper balljoint 57 and the upper arm 51. Accordingly, the vehicle body load andthe carrying load to be transmitted through the suspension cylinder 53hardly act on the upper arm 51, but are transmitted to the tires 11, 12through the casing 56 to which the upper ball joint 57 is provided.Consequently, since the carrying load is not transmitted to the upperarm 51 and the lower arm 52, respective structures of the upper arm 51and the lower arm 52 can be simplified.

Herein, when the vehicle body 10 is moved up and down along with theup-and-down motion of the upper arm 51 and the lower arm 52, apositional relationship between the tires 11, 12 and the electric motor43 is slightly shifted. The drive shaft 18 is connected to an outputshaft 43A of the electric motor 43 and an input shaft 14A of the finalreduction gear 14 via a universal joint in order to absorb the shift ofthe tires 11, 12 from the electric motor 43, and is structured in such aslide type that the drive shaft 18 is extendable and contractible in anaxial direction in order to absorb a changed amount of a distancebetween the vehicle body frame 20 and the casing 56 to be generated whenthe tires 11, 12 move up and down.

Although the drive shaft 18 is shown horizontal in FIG. 5 forconvenience, when no load is placed in the body 30, as shown in FIG. 6,the drive shaft 18 is actually inclined at an intersection angle α1relative to the horizon with a distal end of the drive shaft 18 near thetire 11 facing downward. On the other hand, when the maximum load withinthe allowable load is placed in the body 30, the drive shaft 18 isinclined at an intersection angle α2 relative to the horizon with thedistal end of the drive shaft 18 near the tire 11 facing upward. Theintersection angles α1 and α2 are preferably in a range from 2.5 degreesto 3.5 degrees. In the exemplary embodiment, both of the intersectionangles α1 and α2 are approximately 3 degrees. The intersection angles α1and α2 are set by adjusting a strength of the suspension cylinder 53 oradjusting a distance between the connecting bracket 54 and thesuspension support 205 that are connected by the suspension cylinder 53.

With the above arrangement, a change in the inclination angle of thedrive shaft 18 relative to the horizon between when the load is placedand when no load is placed can be decreased, thereby inhibitingtorsional vibration of the drive shaft 18 during travelling. Forinstance, if the drive shaft 18 is arranged to be horizontal at theintersection angle α1 of zero degree when no load is placed, the driveshaft 18 becomes largely inclined relative to the horizon at an angleclose to the intersection angle α2 of about 6 degrees when the maximumload is placed, so that the torsional vibration during travelling isincreased to reduce durability. In other words, when the drive shaft 18is largely inclined, even during a constant speed travelling in which anangular speed ω1 of the output shaft 43A and an angular speed ω3 of theinput shaft 14A are kept constant, an angular speed ω2 of the driveshaft 18 is changed depending on the size of the intersection angles α1and α2, resulting in generation of torsional vibration. In the exemplaryembodiment, such generation of torsional vibration can be inhibited toimprove durability and the above-described universal joint can beemployed well instead of an expensive constant-velocity joint capable ofabsorbing a large inclination angle.

Incidentally, for the sake of an easy understanding of the intersectionangles α1 and α2, the intersection angles α1 and α2 are exaggeratinglyshown in FIG. 6 to be larger than the actual angles.

Explanation of Steering Mechanism

FIG. 7 is a cross-sectional view showing the steering mechanism, whichis viewed in a direction indicated by an arrow VII-VII in FIG. 4.

As shown in FIGS. 4 and 7, the steering mechanism is configured to moveall the tires 11 and 12 using respective steering cylinders 61. Thesteering mechanism includes the steering cylinders 61 each having aproximal end attached to the upper arm 51 and a distal end attached tothe casing 56.

Specifically, the bifurcated upper arm 51 integrally includes a cylinderattachment arm 55 having an L shape in a plan view. The cylinderattachment arm 55 horizontally extends inward from one of the proximalends of the upper arm 51 to extend over the upper support 207 on thevertical member 202. Moreover, the casing 56 integrally includes aknuckle arm 56B extending in the same direction as the distal end of thecylinder attachment arm 55 in the plan view. The proximal end of thesteering cylinder 61 is attached to the cylinder attachment arm 55 whilethe distal end of the steering cylinder 61 is attached to the knucklearm 56B.

Moreover, a steering arm 56C extending in the travel direction in theplan view is integrally formed to the lower portion of the casing 56.The steering arm 56C includes first and second steering arms 56C in thevehicle width direction. The first and second steering arms 56C areconnected by a pair of tie rods 62, 62 (on the sides) and a bell crank63 (in the middle). By advancing and retracting each of the steeringcylinders 61, the tires 11, 12 with the respective casings 56 aresteered around the king pin shaft 56A via the knuckle arm 56B. Thismovement is mutually transmitted to the casings 56 in pair via the tierods 62 and the bell crank 63, so that both the tires 11 (12) aresteered in conjunction with each other.

Further, a distal end of the knuckle arm 56B is bent upward. A height ofa connecting portion between the knuckle arm 56B and the steeringcylinder 61 is set substantially the same as a height of the rotationcenter of the upper arm 51 and the casing 56, specifically, a height ofthe rotation center 57A of the upper ball joint 57. Accordingly, viewedin the travel direction, an axial line 61A of the steering cylinder 61overlaps a line 51A passing through the rotation center 57A andtraversing a motion center 207A of the upper arm 51 on the upper support207. The respective up-and-down motions of the upper arm 51 and thesteering cylinder 61 are exactly the same. Accordingly, respectiveup-and-down motion regions to be required for the upper arm 51 and thesteering cylinder 61 to move up and down are the same when viewed in thetravel direction (see FIGS. 5 and 7).

In this arrangement, the steering cylinder 61 is disposed adjacent tothe lower cross member 201 along the vehicle width direction. On thelower cross member 201 near the second vertical frame 22, in otherwords, on the lower cross member 201 supporting the lower end of thehoist cylinder 35, the steering cylinder 61 is disposed opposite thehoist cylinder 35 in the travel direction across the lower cross member201, in order to avoid interference with the hoist cylinder 35.

In the exemplary embodiment, since the proximal end of the steeringcylinder 61 is attached not to the vehicle body frame 20 but to thecylinder attachment arm 55 integrated with the upper arm 51, even whenthe suspension 50 including the upper arm 51 is operated, a distancebetween the knuckle arm 56B and the cylinder attachment arm 55 of theupper arm 51 is hardly changed. Accordingly, a relationship betweensteering amounts of the respective tires 11, 12 and advancing andretracting amounts of the respective steering cylinders 61 becomesclear, so that advancing or retracting of the steering cylinders 61 forobtaining desired steering amounts of the steering cylinders 61 can beeasily controlled.

Explanation of Support Structure and Cooling Structure of Electric Motor

FIG. 8 is a cross-sectional view showing a support structure and acooling structure of the electric motor 43.

As shown in FIG. 8, the electric motors 43 are housed in both sides of ahollow portion of the lower cross member 201 on which each of the firstvertical frame 21 and the second vertical frame 22 stands. Openings 209are provided on both sides of the lower cross member 201. Each end of abody of the electric motors 43 close to the output shaft 43A is fixedaround each of the openings 209 by an appropriate fastening unit.

Inside the lower cross member 201, a projection 210 projects from aninner surface of the hollow portion toward each of the electric motors43. Accordingly, an end of each of the electric motors 43 opposite theoutput shaft 43A is supported by the inner surface of the hollow portionthrough the projection 210. The projection 210 is provided by aplurality of projections spaced from each other in a circumferentialdirection. Since the electric motors 43 are housed inside the lowercross member 201 and fixed to the lower cross member 201, the lowercross member 201 itself is reinforced by the electric motors 43, so thatrigidity of the lower cross member 201 is improved.

An inflow port 211 for taking in a cooling air is provided on a centertop of the lower cross member 201 in the vehicle width direction. Acooling blower 71 is attached at a position corresponding to the inflowport 211. Moreover, a predetermined gap (not shown) for discharging thecooling air to the outside is formed at each of fastening parts betweenthe electric motors 43 and both the sides of the lower cross member 201.The cooling air supplied from the cooling blower 71 flows from theinflow port 211 to a space between a pair of electric motors 43 insidethe lower cross member 201, and is subsequently branched toward theelectric motors 43. The branched cooling air passes between theprojections 210 to enter a space between the electric motors 43 and thelower cross member 201, flows to the ends while cooling the electricmotors 43 from an outer circumference thereof, and flows to the outsidefrom the gaps on both the sides of the lower cross member 201.

In the exemplary embodiment, the hollow portion of the lower crossmember 201 defines a duct 72 configured to circulate the cooling air.

The arrangement for flowing the cooling air to the outside is notlimited to the arrangement for flowing the cooling air to the outsidefrom the gaps on the fastening units between the lower cross member 201and the electric motors 43. A plurality of outflow openings, throughwhich the cooling air is discharged, may be provided on both the sidesof the lower cross member 201.

Explanation of Layout of Devices

FIG. 9 is a plan view showing a layout of the devices 41 to 49.

As shown in FIG. 9, the devices 41 to 49 are disposed on the vehiclebody frame 20 as follows in consideration of a weight balance andmaintenance capability of the vehicle body 10. Specifically, in theorder from the first travel direction of the vehicle body frame 20 (inthe order from the left to the right in FIG. 9), the controller 49, apair of electric motors 43, 43 configured to drive the tires 11, theengine 41, the generator motor 42, a pair of electric motors 43, 43configured to drive the tires 12, and a second controller 49 aredisposed substantially in alignment. The engine 41 is the heaviestdevice among the above devices and is disposed closer to the middle ofthe vehicle body frame 20 than the first vertical frame 21.

In the middle of the vehicle body frame 20 in the travel direction, at aposition outwardly away from the vehicle body frame 20 in the firstvehicle width direction, the first radiator 44 for the engine 41 isdisposed and the first cooling fan 45 is disposed to an inner side ofthe first radiator 44. At a position outwardly away from the vehiclebody frame 20 in the second vehicle width direction, the second radiator46 for the water-cooling type aftercooler 41A is disposed and the secondcooling fan 47 is disposed to an inner side of the second radiator 46.

The first and second radiators 44 and 46 are substantially the same insize and the first and second cooling fans 45 and 47 are substantiallythe same in size. The first and second radiators 44 and 46 are disposedsymmetrically with respect to the above-described second center line 10Band the first and second cooling fans 45 and 47 are disposedsymmetrically with respect to the above-described second center line 10B(see FIG. 4). The first and second cooling fans 45 and 47 are suctionfans. A cooling air sucked from the outside and having been subjected toheat exchange with the cooling water of the engine 41 at the first andsecond radiators 44 and 46 and a cooling air having been subjected toheat exchange with the cooling water of the aftercooler 41A aredelivered toward the engine 41 and the generator motor 42 provided inthe middle of the vehicle body frame 20 to cool the engine 41 and thegenerator motor 42 from outer sides thereof.

A pair of brake resistors 48, 48 covered with respective exterior coversare disposed on the second radiator 46 and the second cooling fan 47(see FIG. 1). Cooling fans (not shown) configured to respectively coolthe brake resistors 48 are housed inside the respective exterior covers.Such cooling fans are discharge fans. The brake resistors 48 arecollectively disposed on one side of the vehicle body frame 20 in orderto put priority on maintenance capability. Since the brake resistors 48have a light weight compared with those of the other devices, a weightbalance of the vehicle body 10 is less affected even by the dispositionof the brake resistors 48 only on the one side of the vehicle body frame20.

The first and second radiators 44 and 46, the first and second coolingfans 45 and 47, and the brake resistor 48 are mounted on the supportframe 81. The support frame 81 is fixed to the lower side member 23 andthe upper side member 24 of the vehicle body frame 20 by a fasteningunit (e.g., a bolt).

At the outside of the vehicle body frame 20 in the first vehicle widthdirection, the first radiator 44 and the first cooling fan 45 bridgeover a pair of L-shaped frames 85 juxtaposed in the travel direction tobe supported by the frames 85 and are disposed in an area between thetires 11 and 12. The first radiator 44 and the first cooling fan 45 aremounted in the middle of the vehicle body frame 20 in the traveldirection via the support frame 81 (see the first center line 10A inFIG. 1).

Similarly, at the outside of the vehicle body frame 20 in the secondvehicle width direction, the second radiator 46 and the second coolingfan 47 bridge over the pair of L-shaped frames 85 juxtaposed in thetravel direction to be supported by the frames 85. The second radiator46 and the second cooling fan 47 are disposed in an area between thetires 11 and 12. The second radiator 46 and the second cooling fan 47are mounted in the middle of the vehicle body frame 20 in the traveldirection via the support frame 81 (see the first center line 10A inFIG. 1).

Attachment Position of Hoist Cylinder and Relationship Between HoistCylinder and Engine

FIG. 11 is an illustration of an attachment position of the hoistcylinder 35 in the travel direction, which is viewed in a directionindicated by an arrow XI-XI in FIG. 4. FIG. 12 is a side view showingthe attachment position of the hoist cylinder 35. However, the steeringmechanism is not shown in FIG. 11.

As shown in FIGS. 11 and 12, upper ends of the pair of hoist cylinders35 are rotatably attached to the attachment portions 36 provided in themiddle of the lower surface of the body 30. At the second side of thevehicle body frame 20, a pair of hoist supports 212 are juxtaposed inthe vehicle width direction on the lower cross member 201 on which thesecond vertical frame 22 stands. The lower ends of the pair of hoistcylinders 35 are rotatably supported by the respective hoist supports212 to be supported near the set positions of the tires 12 in the traveldirection. The hoist cylinders 35 set at such positions are supportedwith a large distance from the engine 41 and the generator motor 42connected to the engine 41 near the hoist cylinders 35.

The hoist supports 212 are respectively provided at the positions wherethe electric motors 43 are housed in the lower cross member 201, inother words, at the positions reinforced by the electric motors 43 inthe lower cross member 201. Moreover, the lower cross member 201 is amember on which the second vertical frame 22 provided with the bodysupport 206 stands. Accordingly, the portion to receive the carryingload of the standing body 30 is focused on the second vertical frame 22and the lower cross member 201 positioned between the right and lefttires 12. The carrying load is transmitted from the body supports 206and the hoist supports 212 of the hoist cylinders 35 to the road surfaceimmediately under the tires 12 through the suspension 50 and the tires12. The carrying load does not act on the lower side member 23 and theupper side member 24 (see FIG. 12).

As shown by solid lines in FIG. 12, the body 30 is raised in the secondtravel direction by extending the hoist cylinder 35, thereby performingan unloading operation. When the body 30 is sufficiently raised at orexceeding a predetermined angle, the hoist cylinders 35 substantiallyvertically stand. In such a condition, a large open-top space is definedfrom the first vertical frame 21 to the middle of the vehicle body frame20, in other words, above the portion where the engine 41 is mounted.Since the body 30 and the hoist cylinders 35 are not present in thisspace, the engine 41 disposed near the middle of the vehicle body frame20 can be suspended with a wire or the like with use of this space andis configured to be moved up and down while being suspended when theengine 41 is detached and attached for maintenance.

In addition, the engine 41 is disposed in a region defined by the firstvertical frame 21, the second vertical frame 22, a pair of right andleft lower side members 23, and a pair of right and left upper sidemembers 24. As shown in FIG. 12, there is an open space between thelower side members 23 and the upper side members 24 so that the engine41 is accessible from the outside of the vehicle body frame 20. Withthis arrangement, even while the engine 41 is mounted on the vehiclebody frame 20, maintenance of the engine 41 can be easily conducted fromthe right and left sides of the vehicle body frame 20.

Travelling of Driverless Dump Truck

The above-described dump truck 1 travels between a loading site wheredug minerals are taken in the dump truck 1 as a load and an unloadingsite where the load is unloaded. At this time, when the dump truck 1travels on an outward road toward the unloading site, the side of thedump truck 1 supporting the body 30, in other words, near the secondvertical frame 22 is defined as the back (rear) of the dump truck 1 andthe side thereof near the first vertical frame 21 is defined as thefront of the dump truck 1. When the dump truck 1 travels on a returnroad after the unloading, since the dump truck 1 is not turned around,the side of the dump truck 1 near the second vertical frame 22 isdefined as the front of the dump truck 1 and the side thereof near thefirst vertical frame 21 is defined as the back (rear) of the dump truck1 (shuttle travelling).

However, the dump truck 1 may be turned around as needed and travel witheither the first vertical frame 21 or the second vertical frame 22constantly defined as the front of the dump truck 1.

It should be understood that the scope of the invention is not limitedto the above-described exemplary embodiment(s) but includesmodifications and improvements as long as the modifications andimprovements are compatible with the invention.

For instance, in the above exemplary embodiment, the electric motor 43is configured to drive the tires 11 and 12. However, a driving unit forthe tires 11 and 12 is not limited to the electric motor 43, but ahydraulic motor may replace the electric motor 43.

Moreover, instead of housing the hydraulic motor or the electric motorin the lower cross member 201, the hydraulic motor or the electric motormay be disposed inside the tires 11 and 12 to be defined as an in-wheelmotor.

Further, a driving force of the engine 41 may be transmitted via adifferential device and a drive shaft to drive the tires 11 and 12.

In the above exemplary embodiment, the suspension 50 is provided by adouble wishbone type suspension including the upper arm 51 and the lowerarm 52. However, the suspension of the invention is not limited to thedouble wishbone type suspension. For instance, the suspension 50 may beprovided by a McPherson strut type suspension including an up-and-downmovable arm supported by the lower portion of the vehicle body frame 20and a suspension cylinder connecting the upper portion of the vehiclebody frame 20 to the arm. In this arrangement, the proximal end of thesteering cylinder is supported by the arm.

In the above exemplary embodiment, the body support 206 supporting thebody 30 in a manner to raise or lower the body 30 is provided on thesecond vertical frame 22 disposed in the second travel direction, andthe lower ends of the hoist cylinders 35 for raising and lowering thebody 30 are supported by the lower cross member 201 on which the secondvertical frame 22 stands. However, the lower ends of the hoist cylinders35 may be supported by the lower cross member 201 on which the firstvertical frame 21 stands. In this arrangement, on the lower cross member201 near the first vertical frame 21, it is only necessary to disposethe steering cylinder 61 opposite the hoist cylinders 35 in the traveldirection across the lower cross member 201, in order to avoidinterference between the steering cylinder 61 and the hoist cylinders35.

In addition, the above exemplary embodiment is not exhaustive, but itmay be determined accordingly in each case which portion of the upperarm 51 is attached with the proximal end of the steering cylinder 61 orwhich position is set as the connecting position between the steeringcylinder 61 and the knuckle arm 56B.

The invention is also applicable to a manned off-road dump truckincluding a cab.

The invention claimed is:
 1. A dump truck comprising: a vehicle bodyframe; a suspension; a steering mechanism; tires suspended from thevehicle body frame via the suspension and configured to be steered bythe steering mechanism and travel the dump truck; and a body supportedby the vehicle body frame and configured to be raised and lowered, thesuspension comprising: a suspension arm comprising an up-and-downmovable proximal end supported on the vehicle body frame; and a tiresupport rotatably attached to a distal end of the suspension arm, thesteering mechanism comprising: a steering cylinder comprising a proximalend attached to the suspension arm and a distal end attached to aknuckle arm provided to the tire support, wherein the suspension armcomprises an upper arm and a lower arm that are each attached to thevehicle body frame, the upper arm being positioned above the lower arm,and the proximal end of the steering cylinder is attached to the upperarm.
 2. The dump truck according to claim 1, wherein the vehicle bodyframe comprises a support that supports the suspension arm such that thesuspension arm is movable up and down, the upper arm comprises asteering cylinder attachment arm extending over the support and furtherextending inward in a vehicle width direction, and the proximal end ofthe steering cylinder is attached to the steering cylinder attachmentarm.
 3. The dump truck according to claim 1, wherein viewed in a traveldirection, the steering cylinder has an axial line overlapping a linepassing through a rotation center of the upper arm and the tire supportand traversing a motion center of the upper arm on the vehicle bodyframe.
 4. The dump truck according to claim 1, wherein the vehicle bodyframe comprises a cross member provided in the vehicle width direction,the cross member supports a lower end of a hoist cylinder configured toraise and lower the body, and the steering cylinder is disposed oppositethe hoist cylinder across the cross member in the travel direction.
 5. Adump truck comprising: a vehicle body frame; a suspension; a steeringmechanism; tires suspended from the vehicle body frame via thesuspension and configured to be steered by the steering mechanism andtravel the dump truck; and a body supported by the vehicle body frameand configured to be raised and lowered, the suspension comprising: anupper arm comprising an up-and-down movable proximal end supported on anupper support provided to the vehicle body frame; a lower arm comprisingan up-and-down movable proximal end supported on a lower supportprovided to the vehicle body frame; and a tire support rotatablyattached between respective distal ends of the upper and lower arms,wherein the upper arm comprises a steering cylinder attachment armextending over the support and further extending inward in a vehiclewidth direction, the steering mechanism comprises a steering cylindercomprising a proximal end attached to the steering cylinder attachmentarm and a distal end attached to a knuckle arm provided to the tiresupport, and viewed in the travel direction, the steering cylinder hasan axial line overlapping a line passing through a rotation center ofthe upper arm and the tire support and traversing a motion center of theupper arm on the vehicle body frame.